1. Field of the Invention
The present invention relates generally to communication circuitry and, more particularly, to a method and apparatus for use in a communication circuit, such as an Ethernet or other network transceiver, for converting single-ended signals to a differential signal.
2. Related Art
In communication transceivers, and particularly in Ethernet transceivers which are capable of transmitting and receiving data at 1000 megabits bits per second, communication is possible in a full-duplex mode. In other words, transmitting and receiving of data can occur simultaneously on a single communication channel. Implementation of such a full-duplex communication channel results in a composite signal (VTX) being present across the output terminals of the transceiver, the composite signal VTX having a differential transmission signal component and a differential receive signal component. In such a communication channel, the received signal (VRCV) is derived by simply subtracting the transmitted signal (VT) from the composite signal VTX that is present at the transceiver output terminals. Hence, VRCV=VTX−VT.
This subtraction can be accomplished by generating a signal (referred to as a replica signal) which substantially replicates the transmitted signal, and canceling or subtracting the generated replica signal from the composite signal VTX at the output terminals of the transceiver. However, the replica signal is generated as two single-ended voltages, such as VTXR+ and VTXR−, whereas the composite signal present at the output terminals of the transceiver is a differential signal. Consequently, in order to cancel the replica signal from the composite signal to thereby obtain the received signal, the two single-ended voltage signals must first be converted to a differential signal that can then be subtracted from the composite signal. This conversion, however, requires additional circuitry which adds to the cost and complexity of the transceiver.